Bacteria of the genus Bifidobacterium are clearly known to have various effects such as improving intestinal flora, improving bowel movement, improving intestinal function, preventing infection, immunostimulation and preventing cancers likewise lactic acid bacteria represented by bacteria of the genus Lactobacillus and the like. These microorganisms are considered to improve intestinal environment, thus contributing to human health.
To obtain the above-described effects with bacteria of the genus Bifidobacterium, it is required to maintain a large number of the viable cell count of the bacteria within products such as fermented milks. Since, however, the bacteria of the genus Bifidobacterium are generally anaerobic bacteria, they are poor in viability, and die rapidly especially under the presence of oxygen.
There are, therefore, proposed methods for enhancing the viability of bacteria of the genus Bifidobacterium in products such as fermented milks prepared by making use of the bacteria. Examples of the methods include those making use of sucrose or sorbitol (D-glucitol) (Patent Document 1), erythritol (Patent Document 2) and lactitol (Patent Document 3).
Further, to provide bacteria of the genus Bifidobacterium in their active state for the consumers, measures are being taken such as putting fermentation products containing bacteria of the genus Bifidobacterium immediately after preparation in a container made of an oxygen-impermeable material to completely block the oxygen from coming into contact with the products. In this method, however, the use of oxygen-impermeable container involves many problems in terms of disposal and cost, and thus, the usability of the container is limited.
Therefore, studies are being made on methods of maintaining the viability of bacteria of the genus Bifidobacterium even under aerobic conditions and several methods have been reported. Specifically, there has been reported a method making use of N-acetylglucosamine, panthotenic acid, panthetine, pantetheine, peptides and lactulose. In this method, however, the materials used are themselves relatively high in costs, and when they are used in foods, the flavor and taste of the foods is profoundly affected. Therefore, taking into consideration the effects for the viability of the bacteria as well, there has been a desire for a more convenient material.
It is considered that the viability of bacteria of the genus Bifidobacterium is influenced by the strains used, pH of products (beverages, foods and the like), sugars added as a sweetener, the amount of dissolved oxygen and the like. In order to improve this, considerations are being made on addition of yeast or lactic acid bacteria, combined use of vitamin C, the material of the product container and the like. However, to meet the consumer preference that is becoming diversified recently and the requirement to further improve the viability of the bacteria, there is a desire for a material which can be used for viability improvement.
[Patent Document 1] JP-A-57-004291
[Patent Document 2] JP-B-2577692
[Patent Document 3] JP-B-3261571